Airplane engines can create substantial noise pollution. One way of attenuating this noise is to provide engine nacelles with noise-absorbing composite acoustic panels. Such a panel typically comprises one or more noise-trapping cellular core layers (sometimes referred to as “honeycomb”) covered on a first side by a perforated air-permeable skin (“perf skin”), and on an opposite second side by an air-impermeable skin (“back skin”) The panel is typically assembled by arranging the various core layers and skins on a tool, applying an adhesive, and processing the assembly under a vacuum bag in an oven or autoclave so as to compress the layers and skins together, polymerize the adhesive, and create a single composite structure. However, during the curing process a release agent applied to the tool may potentially migrate, especially if it is partially vaporized by the heat and vacuum used to cure the adhesive, through the holes in the perforated skin and into the panel.
Additionally, composite acoustic panels are often tested by ultrasonic inspection prior to use. Typically, a Through Transmission Ultrasonic (TTU) sender and a TTU receiver are mounted on opposite sides of a panel. The TTU sender and receiver both include water columns that extend to the surfaces of the panel. The TTU sender sends a signal that propagates through its water column, through the panel, and through the TTU receiver's water column to the TTU receiver, and variations in the signal received by the TTU receiver indicate potential flaws in the panel. While the water columns are in contact with the surfaces of the panel, water can migrate through the holes in the perforated skin and into the panel. Water that makes its way into the interior of the panel must be removed before subsequent processing, which may be time-consuming and expensive. Furthermore, water within the panel may fill voids, thus masking defects and making the TTU testing process less effective.
One solution to the problem of water ingression is to apply pressure-sensitive adhesive tape over the holes in the perforated skin immediately prior to TTU testing. More specifically, a technician removes relatively narrow strips of adhesive tape from a roll and places them over the holes with an overlapping pattern. However, this makes inefficient use of the relatively expensive adhesive tape and can cause repetitive motion injuries. Removing the adhesive tape can cause similar injuries due to the high forces necessary to peel the adhesive from the panel. In addition, the perforated skin is sometimes contaminated by the adhesive and must be cleaned with a solvent. Furthermore, the application of adhesive tape does not address the problem of release agent migration. Adhesive tape is applied only to completed panels that have already been assembled (i.e., after any potential release agent migration has occurred).
This background discussion is intended to provide information related to the present invention which is not necessarily prior art.